The invention relates to heart-lung machines including compressed fluid actuated control members.
In heart-lung machines the blood of a patient is transported in an extracorporeal circuit through flexible tubing and medical apparatus, for example an oxygenator. Transporting the blood in the extracorporeal circuit is done by pumps, more particularly roller pumps, in which the rotor acts from without on a portion of the tubing inserted in the stator of the roller pump. When the rollers applied to the rotor roll along the tubing portion, the tubed blood is delivered by displacement at a velocity of up to 3 m/s.
The extracorporeal circuit needs to be controlled which is usually done by directly influencing the pump or with the aid of compressed fluid actuated or electromechanical control members. When use is made of compressed fluid actuated control members, specially adapted flexible tubing needs to be employed. Thus, known from U.S. Pat. No. 5,814,004 is a system for controlling the pressure in an extracorporeal circuit in which compressed fluid actuated valves are provided to influence the circuit. In this system too, the tubing at the locations at which the compressed fluid actuated control members are provided is designed with a thinner tubing wall so that the compressed fluid of the control member is able to mechanically act on the tubing up to a total closing off of the tubing cross-section.
The disadvantage in this and other known systems for controlling the extracorporeal circuit of a heart-lung machine is that specially configured flexible tubing needs to be employed so as to influence the extracorporeal circuit with the aid of the compressed fluid actuated control members. The tubing needs to be configured at the locations at which compressed fluid actuated control members are required to work, with a changed cross-section and/or a reduced wall thickness or made of some other material which not only makes production more expensive but also hampers handling.
Hitherto, however, this disadvantage has been accommodated or recourse made to electromechanical control members capable of also acting on simple flexible tubing, i.e. tubing not specially prepared for cooperation with the control members. This simple tubing, also termed standard tubing, has substantially a constant cross-section and a constant wall thickness and is made with a consistent material composition, i.e. flexible tubing as usually employed in conjunction with heart-lung machines. Preference is given to this simple tubing by users since it is available in any required length or can be cut to length and because the electromechanical control members can be arranged at any location in the tubing.
Both the electromechanical control members and the compressed fluid actuated control members have hitherto not been put to use for time-critical actions in the extracorporeal circuit of a heart-lung machine, more particularly not for instantly closing off the tubing in an emergency situation, for example, when a bubble detector detects bubbles in the blood transported in the extracorporeal circuit. The reason for this, for one thing, is that electromechanical control members are not deemed reliable enough and, for another, that the compressed fluid actuated control members fail to be quick enough in closing off the tubing.
It is against this background that the object to be achieved by the invention is to configure a heart-lung machine including compressed fluid actuated control members so that standard flexible tubing can be put to use without portions specially configured for the effect of the control members and which permits fast reliable influencing, more particularly closing off with the aid of the control members so that it is now possible to achieve time-critical actions, such as, for example, closing off the tubing when an air bubble is detected in the extracorporeal circuit.
This object is achieved by a heart-lung machine having the features as set forth in claim 1. Advantageous aspects read from the sub-claims.
In one special aspect the heart-lung machine in accordance with the invention is configured so that when an air bubble is detected in the extracorporeal circuit the supply of the transported blood to the patient is interrupted without the detected air bubble gaining access to the patient.
The gist of the invention is based on the fact that with the aid of a compressed fluid actuated control member a sufficient energy density can be directly made available for influencing standard flexible tubing for controlling the extracorporeal circuit, for example, for closing it off. It is surprising that there is no indication in prior art of using a compressed fluid whose operating pressure is in the range 2 to 10 bar to thus make it possible to close off flexible tubing as normally used with the aid of a compressed fluid actuated control member whilst also achieving time-critical actions. By the invention recoursing to compressed fluid in cited operating pressure usual flexible tubing, so-called standard tubing can now be put to use with no further change in the cross-section, wall thickness or material. The very high operating pressure as compared to that of prior art permits the extracorporeal circuit to be mechanical effected which not only opens up the basic possibility of controlling the extracorporeal circuit but also accommodating the control of time-critical actions. This is due to the fact that by making use of a compressed fluid in the operating pressure range in accordance with the invention of 2 to 10 bar a positively defined closing condition is now achievable due to the high actuating forces.
It is thus particularly of advantage that a compressed fluid having an operating pressure of approximately 5 bar is regularly available in hospitals so that the heart-lung machine in accordance with the invention can be operated there with no additional complication as regards providing the compressed fluid.
It is also of advantage that the compressed fluid actuated control member in accordance with the invention does not come into contact directly with the blood in the extracorporeal circuit since the effect on the non-specially prepared tubing is always from without.
The high pressure level in accordance with the invention of the compressed fluid permits long supply lines which is particularly of advantage in clinical applications when recourse is made to the compressed fluid available at an operating pressure of 5 bar. The heart-lung machine in accordance with the invention may, however, also be retrofitted with a compressor or pressurized bottle which makes the compressed fluid available at the necessary operating pressure for actuating the control members.
In another advantageous aspect the compressed fluid actuated control members are piston spring systems, because it is particularly control members of this kind that are capable of providing very high forces and very high power at the location of the control member, as a result of which a particularly fast reaction is achieved. Control members configured as piston spring systems are thus particularly suitable for use in time-critical systems, for example in conjunction with a bubble detector.